Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations cover the safety profile (readOnlyHint, openWorldHint), and the description adds genuinely new behavioral context: a concrete cost of '5 credits' and the fact that the numeric user id is the input other tools require, which supports tool chaining. It does not cover error behavior or rate limits, but that is a minor gap given annotation coverage.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two tight sentences: the returned payload first, then the input constraint and cost. Every clause carries information and nothing is padded.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description usefully enumerates the returned fields, and it states cost and the one-of input rule. What remains unstated is failure behavior for missing/invalid identifiers, but for a read-only profile lookup the definition is close to sufficient.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 0% and all three parameters are optional, so the schema does not enforce any selection rule. The description supplies the critical constraint that exactly one of username, user_id or url should be passed, which the schema itself does not express. It stops short of explaining format differences between the three (e.g. URL vs handle).

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific resource and enumerates its contents (bio, follower/following/post counts, links, numeric user id), so an agent knows exactly what comes back. It does not explicitly contrast itself with close siblings like instagramFollowers or instagramMedia, leaving the boundary slightly implicit.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives invocation guidance ('Pass one of username, user_id or url') but no when-to-use or when-not guidance relative to alternatives such as instagramSearch or instagramMedia. Usage is implied by the resource description rather than stated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.